Early detection of the breast cancer is one of the keys to decrease the mortality of this disease. Now more and more attention is paid on development of non-invasive mammography. To study the feasibility of breast imaging with near infrared light, a frequency-domain optical scanner of breast cancer was designed and developed in our lab, based on the theory of interaction of Near Infrared (NIR) light and soft tissues. In this paper, the imaging prototype as well as the imaging processing system based on Matlab is described. The results of phantom experiments using the prototype of this scanner show a resolution in millimeter scale. The initial clinical trials show the feasibility of our prototype in clinical study. The prototype can scan a breast in 4 minutes. Images of the same breast obtained both with the prototype and with x-ray mammography are presented.